List agents

curl --request GET \
  --url https://litellm-rust.onrender.com/api/agents \
  --header 'Authorization: Bearer <token>'

{
  "agents": [
    {
      "id": "<string>",
      "name": "my-agent",
      "model": "claude-opus-4-5",
      "system": "<string>",
      "tools": {},
      "config": {},
      "owner_id": "<string>",
      "status": "paused",
      "description": "<string>",
      "harness": "claude-code",
      "created_at": 123
    }
  ]
}